Clearance of a long steep bank advice please

Can someone please offer me some advice. My garden has a very steep bank approx 10m high and 80m wide. It needs regular clearance of weeds and brambles and is very time consuming and unsightly. The local botanacal gardens have advised planting with Carpobrotus Edulis (Think that was the one). But before I can do this I need to find the quickest and most economical way of clearing the bank of weeds and Ivy etc. Is there a cheap form of weedkiller for large areas such as this?